1. Field of the Invention
The present invention relates to polymeric articles and more particularly relates to lubricious polymeric articles which retain their lubricity during application of sterilizing radiation.
2. Background Art
Semicrystalline polymeric materials, including the polyolefins of which polypropylene is most significant with respect to the present invent ion, are often employed in producing shaped articles subsequently subjected to irradiation sterilization techniques. For example, in the health and medical field, these sterilizable articles include syringes, tubing and tube assemblies, microbiological plastics, flasks, package film and the like. It is well-known that these semicrystalline polymeric materials, if not properly stabilized, will discolor and become embrittled as a result of sterilization by exposure to high energy radiation at levels above 0.1 megarads.
Further, after irradiation has been completed, post irradiative oxidation continues due to free radicals generated by the irradiation which participate in branching chain reactions. Therefore, while degradation of the mechanical properties of these polymeric materials may not be obvious immediately after irradiation, they become more pronounced as time goes on. Thus, much effort has been expended toward agents or additives which would stabilize polymeric materials toward post irradiation degradation.
Some recent attempts have been made to improve the stability of semicrystalline polymeric materials so as to reduce embrittlement. U.S. Pat. No. 4,110,185 to Williams et al. discloses flexible sterilized articles comprising a semicrystalline polymer having a noncrystalline mobilizing additive incorporated therein. The additive increases the free volume of the polymer which is believed to account for the improved stability during and subsequent to irradiation.
In U.S. Pat. No. 4,274,932 to Williams et al., a further improvement in radiation stability is achieved by including the above mobilizing additive in a semi crystalline polymer having a narrow molecular weight distribution.
Polyolefins containing a sterically hindered amine stabilizing agent are disclosed in U.S. Pat. No. 4,785,034 to Gaku et al. in U.S. Pat. No. 4,563,259 to Rayher and in Japanese Patent J60099-147-A.
In addition to a requirement for radiation stability, some articles also require a lubricious surface. U.S. Pat. No. 4,760,116 to Roberts discloses films of crosslinked polyethylene compositions containing fatty acid amide slip agents to provide a satisfactory coefficient of friction (COF).
Articles requiring both sterilization and lubricity at a surface to surface interface, such as a syringe barrel and plunger, present a different problem. Application of a conventional lubricant, such as a hydrocarbon oil or a silicone oil, to the interface has not been satisfactory because many of these lubricants are subject to air oxidation resulting in viscosity changes, objectionable color development, and a tendency to migrate and form beads. For medical articles to be sterilized after packaging, degradation of the lubricant during sterilization or during shelf life may compromise the performance of the article. An approach to overcoming this problem is plasma treatment as disclosed in U.S. Pat. No. 4,767,414 to Williams et al.
In some applications, polymeric materials are used in forms such as plates, sheets, films and the like in which clarity or transparency is a very desirable property. Clarity may also be important for certain plastic articles, such as syringes, made by injection molding. Additives which improve clarity have been disclosed by Hamada et al. in U.S. Pat. No. 4,016,118 by Mahaffey et al. in U.S. Pat. No. 4,371,645 and by Williams et al. in U.S. Pat. No. 4,845,137.
In copending application Ser. No. 362,999, of common assignee herewith, there is disclosed a polyolefin composition of high clarity and stability to radiation sterilization provided by combining the polyolefin with a mobilizing oil, a dibenzylidene sorbitol clarifier and a hindered piperidine stabilizer.
There is a need, unaddressed hitherto in the art, for a lubricious polyolefin composition capable of slidable face-to-face movement over a second surface in an article which can be radiation sterilized after packaging without discoloration, loss of mechanical properties or loss of lubricity. It is toward fulfillment of this need that the present invention is directed.